On 2024/6/27 18:58, Peter Wang (王信友) wrote: > On Thu, 2024-06-27 at 15:59 +0800, Wenchao Hao wrote: >> >> Hi Peter, >> >> What is queue_num's offset of blk_mq_hw_ctx in your machine? >> >> gdb vmlinux >> >> (gdb) print /x (int)&((struct blk_mq_hw_ctx *)0)->queue_num >> $5 = 0x164 >> >> I read your descriptions and wondered a same race flow as you >> described >> following. But I found the offset mismatch, if the racing flow is >> correct, >> then the address accessed in blk_mq_unique_tag() should be 0x164, not >> 0x194. >> Maybe the offset is different between our machine? >> >> What's more, if the racing flow is correct, I did not get how your >> changes >> can address this racing flow. >> >> > > Hi Wenchao Hao, > > Yes, our queue_num's offset of blk_mq_hw_ctx is 0x194. > Our kernel version is: Linux version 6.1.68 > I think the offset is different by kernel version. > > (gdb) print /x (int)&((struct blk_mq_hw_ctx *)0)->queue_num > $1 = 0x194 > > And yes, it only shorten the race window of step3 and step5. > Reduce the probability of step 4 appearing between step 3 and step 5. > > Hi Peter, Thanks for your reply, I understand the issue now. > Thanks. > Peter
